It seems like a slightly more sketchy project than usual, just because everything has to be done so that it'll keep your kid 100% safe. But with that said, child carriers on the market are insanely high weight and I feel like there's got to be a way to improve on them.

The sling won out. Much easier and more pleasant for parent and child. Weight range from newborn to able to walk 3 miles on her own. It works fine with either a courier bag on the opposite shoulder or with a day pack where the bag top is at least a couple inches below shoulder height.

I've seen online patterns. The only caution if you're using slick lightweight fabrics is to make sure that the tail can't slip all the way out of the rings.